THE CII PROTEIN OF BACTERIOPHAGE-186 ESTABLISHES LYSOGENY BY ACTIVATING A PROMOTER UPSTREAM OF THE LYSOGENIC PROMOTER

We have shown previously that the cll gene product of the non-lambdoid temperate bacteriophage 186 is required for the establishment of lyso geny. We show here that CII, a potential helix-turn-helix DNA-binding protein, establishes lysogeny by activating a promoter (p(E)) which sp ans the apl/cll intergenic region, upstream of the lysogenic promoter, p(L) The start site of the p(E) transcript (+1) has been mapped by pr imer extension and we have identified the CII binding determinants at p(E) by DNase I footprinting. CII binds to inverted repeat sequences s eparated by two turns of the helix, with binding half-sites centred at the -38 and -58 positions of p(E). Oligomerisation studies with purif ied CII protein indicate that a CII tetramer may be the species that b inds to this site. We also show that p(E) is subject to direct negativ e feedback by the CI repressor.